The present invention pertains to a direct-current machine comprising a permanent-magnetic stator which contains at least one pair of permanent-magnet shells.
Such direct-current machines are generally known. In most of these direct-current machines, the permanent-magnet shells of a pair of permanent magnets are disposed symmetrically with respect to each other, i.e., their axes of symmetry, which, as a rule, coincide with the direction of magnetization, are in line with each other. It is also generally known that direct-current machines comprising such a stator have a relatively high detent torque or resting moment.
To reduce this detent torque or resting moment, it has already been proposed (DE-OS 25 58 958) to bevel the ends of the permanent-magnet shells to a V-shape in order to thus obtain an oblique stator exciter field. That solution requires specially shaped permanent magnets which have to be produced for that particular purpose. Thus, this known solution is uneconomical at any rate.
Other direct-current machines have become known (DE-GM 70 12 818 and Japanese Kokai No. 53-136609) in which each permanent-magnet shell is divided longitudinally into several permanent-magnet shells which are disposed circumferentially on the stator and are staggered with respect to each other. In this known solution, commercially available permanent-magnet shells can be used, but the assembly of a stator designed in this manner is more complicated and costly.